In the 1940s, harbor porpoise were among the most frequently sighted cetaceans in Puget Sound, but by the early 1970s they had all but disappeared from local waters. Their numbers have since increased, but they remain a Species of Concern in the state of Washington. This in-depth profile looks at harbor porpoise in the Salish Sea, and was prepared by the SeaDoc Society for inclusion in the Encyclopedia of Puget Sound.

A 2014 paper in Endangered Species Research suggests that harbour porpoises inhabiting coastal waters of southern British Columbia constitute a single genetic population, which should be reflected in management decisions.

Description

"Dall’s porpoises are highly acrobatic and are often seen swimming at high speed, darting to and fro, riding the bow waves of boats and engaging in slow rolls at the surface. Because they are black and white, boaters sometimes misidentify them as killer whales. They are small cetaceans, with robust bodies and small heads, flukes, and flippers. Reproductively, they differ from many cetaceans by breeding annually, calving in June or July and mating soon thereafter. This means females are nursing young while pregnant with next year’s offspring. A calf often stays with its mother until the next one is born. Females favor certain areas of the ocean for calving; at calving time, most males, juveniles, and females without offspring stay farther south. Dall's porpoises have very tiny teeth: each tooth is about the size of a grain of rice. They feed on a great variety of prey, from squid to deepwater fish to small schooling fish, which they swallow whole."

Range Description

Dall's porpoises are found only in the northern North Pacific Ocean and adjacent seas (Bering and Okhotsk seas, and Sea of Japan). They inhabit deep waters between about 30°N and 62°N (Jefferson 1988; Houck and Jefferson 1999), but may occasionally occur as far south as about 28°N off the coast of Baja California (Mexico), during unusually cold-water periods.

The dalli-type occurs throughout of the species’ range, from the west coast of North America to Japan.

The truei-type, identified by a broad lateral white patch, inhabits the western north Pacific, and migrates between wintering grounds off the Pacific coast of northern Japan and summer breeding grounds in the central Okhotsk Sea, and constitutes one population (IWC 2002).

Geographic Range

Dall's porpoises, Phocoenoides dalli, are cool water porpoises inhabiting the North Pacific Ocean and adjacent seas. The central Bering Sea marks the northern boundary of their range and, although they prefer colder water, Dall's porpoises are found in the warmer waters of Baja California on the east to southern Japan on the west. They are frequently observed in these lower latitudes during the winter months. There are potentially two subspecies of Dall's porpoises, although they may simply be color morphs, P. dalli dalli and P. dalli truei. Phocoenoides dalli truei is abundant only off the Pacific coast of northern Japan.

Global Range: North Pacific: infrequent north of 62 degrees North in Bering Sea; in west, north of Choshi and east-central Honshu, Japan, and in the Sea of Japan and southern Okhotsk Sea; in east, north from about 28 degrees north (usually north of 32 degrees North). TRUEI morph is most abundant off the Pacific coast of northern Japan and off the Kuril Islands.

Physical Description

Dall's porpoises are the largest of the phocoenids. They typically reach a length of 1.8 to 2.0 meters, rarely more than 2.2 meters. At birth, the length is between 0.85 and 1.0 meters. Weight in adults varies from 130 to 220 kilograms. The body is stocky and more powerful than other members of Phocoenidae. The head is small and lacks a beak although there is a sloping forehead. The flippers are small, pointed, and located near the head. The dorsal fin is triangular in shape with a hooked tip.

There are three color patterns observed in the Dall's porpoises. The first is a uniform black or white throughout the entire body. The second pattern consists of intermixed stripes of black and white running along the length of the body. Finally, there is the most common color pattern observed, that of P. dalli dalli. This is defined as having a dorsal area uniformly black with a white ventral side. The white ventral patch begins far behind the flippers. The dorsal fin, flippers, and fluke are black with some white at the tips. The color pattern of P. dalli truei is different only in the distribution of the white ventral patch. The white patch begins ahead of the flippers rather than far behind them, and P. dalli truei is often longer and slimmer than P. dalli dalli.

Habitat and Ecology

Habitat and Ecology

This species inhabits mainly offshore deep waters colder than 18°C (Miyashita and Kasuya 1988), but may also occur in narrow channels and fjords in the western North Pacific (Jefferson 1988; Rice 1998).

Sex-biased dispersal is known to occur in this species, and this may have relevance in assessing the impact of takes on regional populations (Escorza Trevino and Dizon 2000).

Dall's porpoises are apparently opportunistic feeders, taking a wide range of surface and midwater fish and squid, especially soft-bodied species like lanternfish (myctophids) and gonatid squid. Occasional krill, decapods, and shrimps found in porpoise stomachs are not considered normal prey (Houck and Jefferson 1999; Jefferson 2002).

Habitat

Generally the colder waters of the North Pacific are home to Dall's porpoises. They are observed inshore and offshore. They are a deep water species, so when they approach the coast they usually follow canyons or deep channels. They are also commonly observed in sounds and inland passages where these meet the open sea.

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Details of migrations are poorly known. Year-round resident thoughout much of range, but generally moves north for summer, south for winter. Migrations into Bering Sea may occur spring though fall. Inshore movements may augment populations off California in winter and spring (Leatherwood and Reeves 1983).

Food Habits

Dall's porpoises apparently feed at night and depend to some degree on the deep scattering layer, that is the fauna which travels upwards each night from the deeper parts of the ocean's water column. Food species as determined from stomach contents include squid and other cephalopods, lanternfish, Pacific hake, jack mackerel, herring, sardines, and crustaceans. Dall's porpoises are thought to be capable of deep diving because mesopelagic, bathypelagic, and deep-water benthic species are represented in the diet.

Predation

Killer whales and sharks are believed to be the primary natural predators of Dall's porpoises. They largely escape predation through their large body size, agility in the water, and their habit of traveling in groups. Their coloration may make them difficult to see in the water as well.

Usually travels in groups of 10-20 (also reported as 2-12), though aggregations of at least 200 (or thousands) have been reported. Frequently in association with Pacific white-sided dolphins or pilot whales (Leatherwood and Reeves 1983, Jefferson 1988).

Communication and Perception

As in most phocoenids, Dall's porpoises use a form of echolocation to navigate, capture prey, and perhaps to communicate with conspecifics. They also use a variety of audible clicks and whistles. They may also use touch for social communication.

Reproduction

Little is known about mating in cetaceans, especially in species which occur primarily offshore. Mating systems in Dall's porpoises are unknown.

Little is known about the reproductive biology of Dall's porpoises. Two calving periods have been reported for portions of the eastern North Pacific, one in winter, from February through March, and the other in summer, from July through August. Some segregation of animals seems to occur with juveniles found closer to shore and larger adults well offshore. In offshore areas, females in late pregnancy or lactation seem to be distributed in northern areas, and southern areas are mainly occupied by males and females not accompanied with calves. This seems to indicate that not all females become pregnant every year. Females usually reach sexual maturity between the age of 3 to 6 years, whereas males reach sexual maturity between the ages of 5 to 8 years. Gestation is believed to last about 11 months, and lactation periods are usually about 2 years.

Phocoenoides dalli dalli appear to have three major breeding grounds. Two occur in the North Pacific north of 45 degree latitude, and another breeding site occurs in the central Bering Sea. Phocoenoides dalli truei may breed off the northern coast of Japan.

Breeding interval: Individual females probably do not breed every year. Breeding intervals may be as long as 3 to 4 years because of the length of dependence of calves.

Breeding season: Mating is likely to occur after the calving seasons each year which occur in winter, from February to March, and in summer, from July to August.

Females feed and care for their offspring for extended periods of time. It is likely that some form of extended learning occurs during this period as well. Male parents do not contribute parental care.

Single calf is born mainly late June-September, though births may occur year-round in the eastern North Pacific. Gestation estimates: 7-9 months, 11.4 months. Calves nurse for a few months. Not all adult females become pregnant every year; nonbreeders may segregate from breeders. Males are sexually mature at 5-8 years, females at 3-7 years, depending on location. Most live less than 13 years.

Barcode data: Phocoenoides dalli

The following is a representative barcode sequence, the centroid of all available sequences for this species.

There are 4 barcode sequences available from BOLD and GenBank. Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species. See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

NNTCTATATCTACTATTTGGTGCCTGGGCAGGAATAGTAGGTACCGGCCTAAGCTTATTAATCCGCGCTGAATTAGGTCAACCCGGCTCACTTATTGGAGATGACCAAATCTATAACGTATTAGTAACAGCTCACGCTTTCGTAATAATCTTCTTTATAGTGATACCCATTATAATTGGAGGATTTGGGAACTGACTAGTTCCCTTAATAATTGGAGCCCCTGATATGGCATTCCCTCGTCTAAACAACATGAGCTTCTGACTACTTCCTCCCTCTTTCCTATTACTAATAGCATCCTCCGTAGTTGAAGCCGGTGCAGGCACAGGCTGAACCGTATACCCCCCTCTAGCAGGGAACCTAGCACATGCAGGGGCCTCAGTGGATCTTACCATTTTCTCCCTACATCTAGCCGGAGTGTCTTCAATCCTTGGGGCTATTAATTTCATCACAACTATCATCAACATAAAACCACCTGCTATAACCCAATACCAAACACCTCTTTTCGTGTGATCAGTCCTAGTTACAGCGGTATTACTTTTATTATCACTACCTGTCCTAGCAGCCGGAATTACCATACTATTAACCGACCGAAATCTAAATACAACTTTCTTTGACCCTGCAGGAGGGGGCGATCCTGTCCTATATCAGCACTTANNN-- end --

The species is widespread and abundant, with current range-wide population estimates of more than one million animals. The species was killed in high-seas driftnet fisheries operations during the 1970s and 1980s, but these fisheries have now been banned, and by-catch levels were not considered sufficiently high to cause population declines. While incidental and directed takes in Japanese coastal waters as well as incidental takes in Russian waters are ongoing (with combined removals on the order of 20,000 annually), neither threat is likely to have caused a range-wide decline sufficient to warrant listing in a category of threat.

Conservation Status

Dall's porpoises are not directly exploited in the eastern Pacific, but serious conservation problems are centered in the western Pacific where, during the 1980's, Dall's porpoises were intensely hunted. Estimates suggested 40,367 Dall's porpoises were killed in 1989 from the Japanese hand-harpoon fishery alone. In recent years these numbers have declined because of the Japanese government's effort to regulate the hand-harpooning of these animals. In 1992 11,403 were killed. This species is often killed accidentally in the Japanese seas and off of North America by drift nets set for salmon. It has been estimated that up to 20,000 porpoises are entangled and drowned in these nets off of Japan and up to about 4,100 off of North America annually. Due to international negotiations between Japan and the United States, along with new fishing gear and techniques, the incidental take has been reduced drastically. However, the conservation of Dall's porpoises remains a major issue.

NatureServe Conservation Status

Population

Population

Dall’s porpoises are common in many parts of the North Pacific, and density is high in many areas of the range. The total abundance of the species is probably over 1.2 million individuals (Buckland et al. 1993). In Alaska, the abundance is estimated at 83,400 (CV=10%) (Angliss and Outlaw 2005). Along the U.S. west coast, abundance estimates have ranged from about 35,000 to 134,000, averaging 86,000 animals (CV = 45%) between 1991 and 2005 (Barlow and Forney, in press). In the western North Pacific, the truei-type population migrating between the Pacific coasts of Japan and the central Okhotsk Sea is estimated at 217,000 (CV=0.23). The dalli-type population migrating between the Sea of Japan and the southern Okhotsk Sea is estimated at 226,000 (CV=0.15), and the dalli-type population summering in the northern Okhotsk Sea at 111,000 (CV=0.29) (IWC 1998). These estimates are subject to biases due to response to survey vessels.

The International Whaling Commission currently recognizes 11 populations of this species, based on differences in genetics, pollutant loads, parasite faunas, and distribution patterns of cow/calf pairs (IWC 2002). Three of them summer in the Okhotsk Sea, two in the Bering Sea, four in the North Pacific, and two off the US coast, but the wintering grounds are unknown for many of them. The populations cannot be reliably distinguished by their external appearance at sea except for the three summering in the Okhotsk Sea, which are distinguishable based on the pigmentation and location.

Threats

Major Threats

The largest threats to this species have been incidental takes by salmon and squid drift net fisheries and direct takes by hand harpoon fishery in Japanese coastal waters. The driftnet salmon fisheries began in 1952 and continued until a United Nation moratorium on all high-seas driftnet fisheries came into effect (Reeves et al. 2003). The large-mesh and squid driftnet fisheries operated throughout the central and western North Pacific between about 35˚N and 47˚N, increasing in effort during the 1970s and peaking during the 1980s prior to the moratorium. Bycatch estimates are only available for 1989-1990, when about 4,000 Dall's porpoise were estimated killed per year (Hobbs and Jones 1993). During the 1970s and 1980s, the combined high-seas driftnet fisheries likely killed tens of thousands of Dall's porpoise, but this level would not have been high enough to cause population declines (Hobbs and Jones 1993). The estimated annual take by Japanese salmon fisheries within the United States EEZ for the period 1981-1987 ranged from 741 (1987) to 4,187 (1982), with lower levels of additional takes in Bering Sea waters outside of the U.S. EEZ (IWC 1991; T. Jefferson pers. comm.).

Incidental catches on the order of thousands of porpoise per year are ongoing in several fisheries using gillnets in the Russian exclusive economic zone (Burkanov and Nikulin 2001). Small numbers of Dall's porpoises are also taken along the US West Coast in drift net and trawl fisheries (Carretta et al. 2006).

The Japanese hand harpoon fishery for Dall’s porpoise started in the 1910s (Ohsumi 1972; Sawadate 1983), made a great expansion around the World War II period (Wilke et al. 1953; Sawadate 1983), then remained lower at between 5,000 and 10,000 individuals until the 1970s (Kasuya 1982). Approximately 111,500 Dall’s porpoises were removed by hunting between 1986 and 1989 from two stocks centred in the Okhotsk Sea (IWC 1991). The Japanese government began to regulate the hand-harpoon hunt in 1989, and a catch quota was introduced in 1993. The fishery currently operates with a quota of 9,000 dalli-type Sea of Japan-southern Okhotsk Sea population and 8,700 truei-type Pacific coast-central Okhotsk Sea population (IWC 2002). The current level of reported takes are about 4% of the mean estimate of the size of the populations; however, these catch statistics might not be reliable (Kasuya 2007).

Environmental contaminants are also thought to be a threat, and high levels of organochlorines may reduce testosterone levels in males and affect calf viability, thereby influencing reproduction and survival (Subramanian et al. 1987, 1988).

Comments: Thousands were killed annually in the 1970s and 1980s in the Japanese salmon fishery. Unknown number are taken incidently in squid gillnet fisheries in the western North Pacific. During 1986-1989, in excess of 110,000 were taken directly in Japanese harpoon fishery (IUCN 1991).

Economic Importance for Humans: Positive

The only direct commercial harvest of Dall's porpoises is a traditional coastal harpoon fishery in Japan which accounts for annual harvests of about 6,000 animals to compensate for the shortage of whale meat. Dall's porpoises contribute to marine ecotourism through their gregariousness and their aquatic antics.

false - false - false - Details of migrations are poorly known. Year-round resident thoughout much of range, but generally moves north for summer, south for winter. Migrations into Bering Sea may occur spring though fall. Inshore movements may augment populations off California in winter and spring (Leatherwood and Reeves 1983).

Single calf is born mainly late June-September, though births may occur year-round in the eastern North Pacific. Gestation estimates: 7-9 months, 11.4 months. Calves nurse for a few months. Not all adult females become pregnant every year; nonbreeders may segregate from breeders. Males are sexually mature at 5-8 years, females at 3-7 years, depending on location. Most live less than 13 years.

Ecology Comments:

Usually travels in groups of 10-20 (also reported as 2-12), though aggregations of at least 200 (or thousands) have been reported. Frequently in association with Pacific white-sided dolphins or pilot whales (Leatherwood and Reeves 1983, Jefferson 1988).

North Pacific: infrequent north of 62 degrees North in Bering Sea; in west, north of Choshi and east-central Honshu, Japan, and in the Sea of Japan and southern Okhotsk Sea; in east, north from about 28 degrees north (usually north of 32 degrees North). TRUEI morph is most abundant off the Pacific coast of northern Japan and off the Kuril Islands.